Bed gravity is an irresistible force that draws you back to bed, or toward any mattress, couch, or other soft horizontal surface. It is usually stronger when one or more persons are already sleeping on that furniture.

床重力是一股让你难以抵抗的力量，能将你拉回床、床垫、沙发或者其他一切软的可以平躺的物件上。如果已经有人躺倒在这些物件上，床重力的威力就会更加强大。

For example:

I have to fight bed gravity for at least 30 minutes every morning before struggling to get up.

我每天早晨从床上爬起来之前都至少要跟床重力斗争半个小时。